The present invention relates to an imaging system and more particularly to an office based system which is suitable for making photocopies. In accordance with the invention, images are formed by image-wise exposing a composition comprising a chromogenic material and photosensitive encapsulate to actinic radiation and rupturing the capsules in the presence of a developer whereby a patterned reaction between the chromogenic material and developer is obtained which produces an image. This application specifically addresses transfer systems in which the capsules are ruptured in contact with a developer sheet to which chromogenic material is transferred for the patterned image-forming reaction.
Imaging systems based on photosensitive encapsulates are known. Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which azo-blue-"B" black dye is encapsulated with a cross-linkable polymer or a polymerizable monomer as a fluid-droplet containing film or a fluid droplet containing microcapsules. As described, the Berman imaging system is a transfer system which relies upon selectively transferring the encapsulated dye to a copy sheet in correspondence with the image. Imaging is accomplished by image-wise exposing a layer of the encapsulate to electromagnetic radiation to cross-link the polymer, causing the liquid in the exposed capsules to assume a rigid condition and not transfer to a copy sheet. Dye transfer is limited to the unexposed areas of the encapsulate containing layer.
Phillips, U.S. Pat. No. 3,700,439 discloses a photocopy process wherein Michler's ketone is encapsulated in a conventional manner and provided as a layer on a support. Michler's ketone itself is not a color former, but patterned irradiation of the ketone containing capsules produces a latent image of colorless, acid-colorable, dye precursor from the ketone such that upon contact with an acid developer such as acid clay a visible image is obtained. Phillips discloses both a system wherein the exposed imaging sheet is calendered face-to-face with an acid-coated receiving sheet to form images and a system wherein the acid developer is on the same surface as the capsule coating so that after rupturing the capsules on the imaging sheet there is development without transfer.
Berman et al, U.S. Pat. No. 3,072,481 discloses another type of encapsulated light sensitive element which utilizes a light-sensitive material which is readily converted to a colored form when carried in a liquid vehicle but which is insensitive to light when solid. By encapsulating such a material with a volatile solvent, image-wise exposing a layer of the encapsulate and rupturing the capsules to evaporate the solvent, an image is obtained and fixed.
Forris, U.S. Pat. No. 3,001,873, discloses a more complex system wherein the walls of capsules containing a solid dye are photosensitized such that patterned exposure renders the capsules unswellable. By wetting the sheet to swell the unexposed capsules and heating, the dye is immobilized in the unexposed areas. Thereafter, by rupturing the capsules in contact with a receiving sheet there is an image-wise transfer of the dye from the exposed areas only.
While image-forming techniques such as these have been known, for various reasons, they have not matured into commercial photocopy systems. Furthermore, the potential of these systems to afford a low cost imaging system has not been realized.